Mole-Mole Ratio lab.docx

# 5 immerse the tip of the temperature probe in the

• Lab Report
• 10

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5. Immerse the tip of the temperature probe in the polystyrene cup of NaOCl solution. 6. Measure out precisely 25.0 mL of the 0.50 M Na2S2O3 solution into a beaker. Do not mix the two solutions yet. 7. Start the data collection. Let the program gather and graph a few initial temperature

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SHOULD I GET MY MOLE CHECKED OUT? readings, and then add the Na2S2O3 solution. Gently stir the reaction mixture with the temperature probe. 8. Examine the data to calculate and record the maximum temperature change. 9. Rinse out and dispose of the reaction mixture as directed. 10. Continue testing various ratios of the two solutions, keeping the total volume constant, until you have 3 measurements on either side of the ratio that produced the greatest temperature difference. DATA TABLE Trial Volume OCl - (mL) Volume S 2 O 3 2- (mL) Maximum Temperature Change ( C) 1 2 3 4 5 6 7
SHOULD I GET MY MOLE CHECKED OUT? PRE-LAB QUESTIONS 1. What is the total reaction volume for this procedure? 2. Predict the sign of ΔH for this reaction. Justify your prediction. 3. Using the set of axes provided below, properly label the y-axis and sketch the curve that you expect to see at the end of a given trial. Explain how you will use the graph to determine the maximum temperature change. 4. Explain how you will use this curve to determine the maximum temperature change for a given trial. 5. A student conducts this experiment using two equimolar reactants, X &Y, and obtains the data shown in the table below. The optimum mole-to-mole ratio requires that you plot the maximum temperature change recorded for each trial vs. the volume of X reacting. To determine the optimum ratio, perform two linear regressions for the temperature change vs. volume of reactant X data. One regression will have a positive slope while the other will have a negative slope. Both regressions will involve all the points on the portion of the graph that approaches the maximum. The optimum volume for reactant X is obtained by interpreting the point where the two regression lines intersect. Once you have established the simplest whole number optimum ratio for the reactants, write the moles of reactant X that react completely with reactant Y in the space provided below the data table.

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SHOULD I GET MY MOLE CHECKED OUT? POST-LAB QUESTIONS AND DATA ANALYSIS 1. Use graphical methods to determine the whole number mole ratio of the two reactants in this experiment, based on your data. 2. Why must the total volume of the solution mixture be kept constant in all trials? 3. The molarities of the reactant solutions were equal in this experiment. Is this necessary, or even i mportant, for the success of the experiment? 4. Identify the limiting reactant for each trial that you performed. 5. Write the balanced oxidation-reduction reaction for the reaction of OCl and S 2 O 3 2– in basic solution. Does the mole ratio that you determined in your experiment match the actual reaction equation’s coefficients?
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• Fall '17
• Mr Brown
• Sodium, Chemical reaction, Vernier & Laboratory, Flinn Scientific., equimolar Na2S2O3

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